Interpretive Summary: Emission of PM10 (particulate matter smaller than 10 micrometers in diameter) from agricultural soils has resulted in exceedance of the US EPA air quality standard for PM10 within the Columbia Plateau region of the US Pacific Northwest. Soils vary in their particle size composition and consequently in their ability to emit PM10. This variation, however, has not been characterized for the sandy loam and silt loam soils commonly found across the region. We found that sandy loam soils had the greatest potential to emit PM10 even though the sandy loam soils were composed of a smallest percentage of PM10 as compared with the silt loam soils. PM10 emissions were driven by saltation processes in sandy loam soils and by suspension processes in silt loam soils. Results from this study can be used by USEPA, USDA-NRCS, or USDA-ARS scientists to develop a tool for estimating PM10 emissions from soils; these estimates can then be used by atmospheric scientists in regional air quality models for predicting air quality across the region.

Technical Abstract:
Wind erosion and fugitive dust emission from agricultural lands is a concern in the inland U.S. Pacific Northwest because emission of particles with a mean aerodynamic diameter less than or equal to 2.5 µm (PM2.5) and 10 µm (PM10) are stringently regulated by the U.S. Environmental Protection Agency as air pollutants. To predict the emission of PM2.5 and PM10 and consequently the impact on regional air quality, the potential release of PM2.5 and PM10 must be quantified for windblown soils. The objective of this study was to characterize the PM2.5 and PM10 emission potential and rate of soils in the region. Soil from the upper 3 cm layer of the profile was collected from five major soil types in southeastern Washington. The PM2.5 and PM10 fraction along with other particle size distributions of both dispersed and nondispersed soils were respectively measured by laser diffraction and sonic sieving. Soil samples collected from the field were screened to remove plant debris and rocks and placed inside a portable wind tunnel to simultaneously measure PM2.5 and PM10 emissions at three wind speeds. Dispersed soil analysis indicated that the sand and silt content of the five soil types respectively ranged from 17 to 68% and 23 to 66%. Nondispersed soil sieving revealed no significant difference in PM2.5 and PM10 among soils with the PM2.5 and PM10 percentage averaging 1.2% and 3.7%, respectively, and the PM2.5/PM10 ratio ranging from 0.26 to 0.37. Wind-induced particulate emissions were greatest for Warden sandy loam and lowest for Walla Walla silt loam. Across all soil types and at the highest wind speed (18 m s-1), loss of sediment, PM10 and PM2.5 ranged from 113 to 8039 g m-2, 0.4 to 11.0 g m-2, and 0.1 to 6.0 g m-2, respectively. Although PM2.5 and PM10 emissions and the PM10/sediment loss ratio differed among soils, no significant difference was found in the PM2.5/sediment loss ratio across soils. Our results suggest that the emission potential varies for windblown soils found across the inland Pacific Northwest.